Cardiac pacing by an artificial pacemaker provides an electrical stimulation of the heart when the heart's own natural pacemaker and/or conduction system fails to provide synchronized atrial and ventricular contractions at rates and intervals sufficient for a patient's health. Such antibradycardial pacing provides relief from symptoms and even life support for hundreds of thousands of patients.
The rate of stimulation provided by a pacemaker may need to be adjusted to match the level of the patient's physical activity. Prior rate responsive pacemakers have relied on, among other parameters, central venous temperature to indicate the need to adjust stimulation rates up or down. Prior devices often used temperature sensors connected to the pacemaker body by a lead extending from the pacemaker body's location outside of the heart to a temperature sensor located within the patient's heart. Two examples of prior rate-responsive pacemakers may be found in U.S. Pat. No. 5,411,535 and U.S. Patent Publication No. 2007/0088400.